swift - 我的 subview 无法添加到作为 UIView.xib 文件的 subview 的 UIView，它返回 nil

Question

我有两个 Swift 文件，一个名为 FileView.swift，另一个是 FileViewController.swift。使用 MVC 架构，我尝试将 FileViewController.swift 中的 subview 添加到 FileView.swift 的 webViewContainer:UIView!这是来自 XIB 文件的 IBOutlet。

但是，当从 FileViewController.swift 调用它时，我得到的结果为零。

class FileView: UIView {

    @IBOutlet weak var webViewContainerHeight: NSLayoutConstraint!
    @IBOutlet weak var webViewContainerWidth: NSLayoutConstraint!
    @IBOutlet weak var closeBttnWidth: NSLayoutConstraint!
    @IBOutlet weak var closeBttnHeight: NSLayoutConstraint!
    @IBOutlet weak var webViewContainer: UIView!
    @IBOutlet weak var closeButton: UIButton!

    override init(frame: CGRect) {
        super.init(frame: frame)
        setup()
    }

    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
        self.setupNIB()
    }

    private func setup() {
        webViewContainer = UIView(frame: CGRect(x: 0, y: 0, width: 500, height: 350))
    }

class FileViewController: UIViewController, WKNavigationDelegate {

    var webView = WKWebView()
    var campaignUrl = ""
    var finalCampaignUrl = ""

    lazy var customView: FileView = {
        let customView = FileView()
        return customView
    }()

    override func loadView() {
        self.view = self.customView
    }

    override func viewDidLoad() {
        super.viewDidLoad()
    }

    override func viewWillAppear(_ animated: Bool) {
        super.viewWillAppear(animated)
        webViewModal()
    }

func webViewModal () {
        if UIDevice.current.userInterfaceIdiom == .pad {
            let deviceWidth = UIScreen.main.bounds.width/3
            let deviceHeight = UIScreen.main.bounds.height/3
            customView.webViewContainerWidth.constant = 290 + deviceWidth
            customView.webViewContainerHeight.constant = 475 + deviceHeight
            customView.closeBttnWidth.constant = 55
            customView.closeBttnHeight.constant = 55
            customView.closeButton.layoutIfNeeded()
            customView.webViewContainer.layoutIfNeeded()
        }
        webView = Global.setWKWebViewInitWithConfig(frame: .zero)
        customView.webViewContainer.addSubview(webView)
        customView.webViewContainer.showSpinner(CGSize(width: 30 , height: 30), tintColor: UIColor.lightGray)
        webView.translatesAutoresizingMaskIntoConstraints = false
        let webViewHeightConstraint = NSLayoutConstraint(
            item: webView,
            attribute: .height,
            relatedBy: .equal,
            toItem: customView.webViewContainer,
            attribute: .height,
            multiplier: 1,
            constant: 0
        )
        let webViewWidthConstraint = NSLayoutConstraint(
            item: webView,
            attribute: .width,
            relatedBy: .equal,
            toItem: customView.webViewContainer,
            attribute: .width,
            multiplier: 1,
            constant: 0
        )
        let webViewLeftMarginConstraint = NSLayoutConstraint(
            item: webView,
            attribute: .leftMargin,
            relatedBy: .equal,
            toItem: customView.webViewContainer,
            attribute: .leftMargin,
            multiplier: 1,
            constant: 0
        )
        let webViewRightMarginConstraint = NSLayoutConstraint(
            item: webView,
            attribute: .rightMargin,
            relatedBy: .equal,
            toItem: customView.webViewContainer,
            attribute: .rightMargin,
            multiplier: 1,
            constant: 0
        )
        let webViewBottomMarginContraint = NSLayoutConstraint(
            item: webView,
            attribute: .bottomMargin,
            relatedBy: .equal,
            toItem: customView.webViewContainer,
            attribute: .bottomMargin,
            multiplier: 1,
            constant: 0
        )
        NSLayoutConstraint.activate([webViewHeightConstraint, webViewWidthConstraint, webViewLeftMarginConstraint, webViewRightMarginConstraint, webViewBottomMarginContraint])

        webView.navigationDelegate = self

        Global.initialLoadWithParam(ofWebView: webView, withURL: NSURL(string: campaignUrl)!)
        customView.closeButton.layer.cornerRadius = 0.9 * customView.closeButton.bounds.size.width
        customView.closeButton.backgroundColor = #colorLiteral(red: 0.003921568627, green: 0.1647058824, blue: 0.2666666667, alpha: 1)
        customView.closeButton.tintColor = #colorLiteral(red: 1, green: 1, blue: 1, alpha: 1)
        customView.webViewContainer.layer.cornerRadius = 15
        customView.webViewContainer.layer.masksToBounds = true
    }

我预计这应该添加

webView = Global.setWKWebViewInitWithConfig(frame: .zero)

至

customView.webViewContainer.addSubview(webView)

但它在 customView.webViewContainer 的行上返回 nil:

Thread 1: Fatal error: Unexpectedly found nil while implicitly unwrapping an Optional value

当在重写函数 loadView() 上加载 customView 时，webViewContainer 不应该已经实例化吗？

Answer 1

问题是你的webViewContainer是 weak引用:

class FileView: UIView {
    // ...
    @IBOutlet weak var webViewContainer: UIView!
    // ...
}

如果

这工作正常

• 您正在使用 XIB 文件
• 某人(例如 View Controller )保留对顶 View 的强引用
• 导出是 View 层次结构的一部分。

但就你而言，在 setup您创建 View 的实例，将其存储在弱引用中，然后 ARC(引用计数机制)将发现不再有对 UIView 的强引用。因此清除内存，导致 nil引用。

所以你需要以某种方式保留一个强有力的引用；在最简单的情况下，只需跳过 weak导出中的引用说明符。

但请记住，您可能需要执行其他操作来防止强引用循环。就您而言，如果您不使用 xib文件，您可以删除所有 @IBOutlet东西并制作 NSCoder初始化程序只需调用 fatalError ，以防止从 xib 进行任何创建文件。